Already well known amorphous magnetic materials are mainly alloys of a magnetic metal atom and a metalloid atom (for example, B, C, Si, Al, Ge, Bi, S, P, etc.), for example, Fe.sub.80 B.sub.20, (Co.sub.0.94 Fe.sub.0.06).sub.79 Si.sub.10 B.sub.11 or Fe.sub.80 P.sub.13 C.sub.7.
In these alloy systems, the sizes of the metal atoms and the metalloid atoms are greatly different and therefore it has been considered that these alloys can be made easily amorphous. However, these conventional amorphous alloys contain a large amount of metalloid atoms which relatively readily move at low temperatures, as the composing atoms, so that these amorphous alloys have the drawbacks that the properties possessed by these alloys, particularly the magnetic property, are noticeably varied with lapse of time. For example, in the case of amorphous alloy of (Co.sub.0.94 Fe.sub.0.06).sub.79 Si.sub.10 B.sub.11 consisting mainly of Co, which has high magnetic permeability, the effective magnetic permeability .mu.e immediately after heat treatment at 20 KHz is 16,000, but the permeability after keeping at 150.degree. C. for 100 hours is deteriorated about 50% and .mu.e becomes 8,000. This deterioration is presumably caused by transfer of the metalloid atoms of B, Si, etc. Accordingly, the amorphous alloy having such a high deterioration with lapse of time cannot be practically used as the core for a magnetic head.
Therefore, the inventors have provided an invention by which the drawbacks of the above described conventional alloys have been obviated and filed the invention as Japanese Patent Application No. 121,655/79. The alloys of the above described invention are metal-metal system amorphous alloys wherein the conventional metalloid atoms are substituted with Zr, Hf, Ti and Y, and are characterized in that the conventional metalloid atoms are not substantially contained, so that the thermal stability is high and the deterioration with lapse of time is very low.